In recent years, there has been an increasing demand for information equipment, such as digital electronic still cameras, digital video cameras, mobile phones, and PDAs (Personal Digital Assistants), having a capturing function in accordance with high resolution of solid-state imaging devices such as CCD (Charge Coupled Device) area sensors, and CMOS (Complementary Metal Oxide Semiconductor) image sensors. Furthermore, the information equipment having the above-described capturing function is referred to as an imaging device.
As a technique relating to this type of imaging device, however, there is a known technique which performs focusing control by detecting a phase difference using image information obtained by the solid-state imaging element (performs AF (Auto Focus) control by a so-called phase-difference AF system) to provide an imaging device capable of performing AF control with high accuracy.
The principle of the phase-difference AF system will be described below.
As an example, as illustrated in FIG. 15, light from a specific point on an object is divided into a beam ΦLa that passes through a pupil corresponding to point “A” and enters the point “A” and a beam ΦLb that passes through a pupil corresponding to point “B” and enters the point “B”. Since these two beams are emitted from one original point, if a focal point of a camera lens matches on a light receiving surface (imaging surface) of the solid-state imaging device, the two beams will arrive at one point on the same microlens as illustrated in FIG. 15A. However, for example, if the focal point of the camera lens is formed in front, by an “x” distance, from the light receiving surface of the solid-state imaging device, the two beams are misaligned from each other by 2θx, as illustrated in FIG. 15B. Therefore, if the focal point of the camera lens is formed at a back side, by the “x” distance, from the light receiving surface of the solid-state imaging device, arrival points of the beams are misaligned from each other by 2θx in the reverse direction.
Based on this principle, an image formed by an alignment of points “A” and an image formed by an alignment of points “B” match with each other if the camera lens is in-focus, and the images are misaligned with each other if the camera lens is out of focus.
As techniques based on this principle, techniques disclosed in Patent Document 1 (Japanese Patent Application Laid-Open (JP-A) No. 2002-14277), Patent Document 2 (JP-A No. 2010-107770), and Patent Document 3 (JP-A No. 2006-208495) are known. Patent Document 1 (JP-A No. 2002-14277) discloses a technique including: comparing two images formed by light which passes through pupils of different positions in a capturing lens; correcting at least one of the two images based on the comparison result; and detecting a focal point of the imaging lens by performing a correlation computation on the corrected image signal.
Further, Patent Document 2 (JP-A No. 2010-107770) discloses an imaging device including: a photoelectric conversion unit that is provided with a first pixel group which photoelectrically converts an object image from a first exit pupil region of an imaging lens and a second pixel group which photoelectrically converts an object image from a second exit pupil region different from the first exit pupil region; a focus detection unit that performs focus detection of the capturing lens using a first image signal obtained from the first pixel group and a second image signal obtained from the second pixel group; a calculation unit that calculates an inclination with respect to an alignment direction of pixels of the first and second pixel groups, which is a straight line formed by joining a center of the first exit pupil region and a center of the second exit pupil region; and a focus detection range setting unit that sets a focus detection range based on the calculation result by the calculation unit.
Further, Patent Document 3 (JP-A No. 2006-208495) discloses a focus detector provided with a reimaging lens that reimages a beam transmitted through a capturing lens and a plurality of photoelectric conversion units that receive the reimaged beam through a microlens and convert the received beam into an image signal, wherein the focus detector includes a focus state detection unit that detects a focus state of the capturing lens based on the converted image signal. In this focus detector, the reimaging lens has a plurality of pupil regions which transmit the beam transmitted from the imaging lens, the plurality of photoelectric conversion units each receive the beam transmitted from the pupil region through the microlens and each convert the received beam into the plurality of image signals, and the focus state detection unit detects the focus state of the capturing lens based on a relative positional relationship of the plurality of image signals which are each converted by the plurality of photoelectric conversion units.
However, in all of the techniques disclosed in Patent Document 1 (JP-A No. 2002-14277), Patent Document 2 (JP-A No. 2010-107770), and Patent Document 3 (JP-A No. 2006-208495), since a pupil split is performed, a light quantity received by the solid-state imaging element of point “A” and a light quantity received by the solid-state imaging element of point “B” are different from each other depending on an incident angle, as illustrated in FIG. 15, and in a general capturing lens, for example, the light quantity (sensitivity) received by point “A” is different from the light quantity (sensitivity) received by point “B” in a central portion and circumferences of an angular field, as illustrated in FIG. 16. Therefore, since the light quantity greatly depends on the incident angle of incident light and the solid-state imaging element, in general, each electric signal output from each solid-state imaging element of points A and B is subjected to the correlation computation after correction processing.